1. Field of the Invention
Embodiments of the present invention relate to encoding and decoding speech signals, and, more particularly, to speech signal compression and/or decompression methods, media, and apparatuses in which the speech signal is transformed into the frequency domain for quantizing and dequantizing information of frequency coefficients.
2. Description of the Related Art
Currently, there are various techniques for speech signal compression and decompression based on frequency transform. These basic compression techniques typically include implementing a frequency transform module, a band division module, a bit allocation module, and a frequency coefficient quantization module. The frequency transform module receives a speech signal, in a duration unit, and transforms the speech signal into the frequency domain through a single transform procedure to obtain frequency coefficients. The frequency coefficient quantization module individually quantizes the frequency coefficients. If the duration unit for the frequency transform becomes too short, the correlation between speech signals in the time domain cannot be sufficiently used, which results in a reduction in the effect of the frequency transform and lowering quantization efficiency. If the duration unit for the frequency transform becomes too long, changes in the characteristics of the speech signals in the time domain disappear, which results in a reduction in the effect of the frequency transform, lowering quantization efficiency, and increasing time delay and complexity in the compression procedure. In other words, since quantization efficiency depends on the duration unit for the frequency transform, it is difficult to obtain optimal compression performance.
Characteristics of the speech signal continuously vary over time. In particular, a duration having a very stably repeated characteristic and a duration having an irregularly and suddenly varied characteristic both coexist in the speech signal. Accordingly, it becomes necessary to positively take advantage of a time-varying property of the speech signal in the frequency transform procedure, so that the optimal effect of the frequency transform can be always obtained, thereby enhancing the quantization efficiency and achieving high compression performance.